Butter a 15x10x1 jelly roll pan, line with wax paper, butter paper. Sift flour, baking powder and salt onto wax paper. Beat the egg whites in a medium bowl with electric mixer on high speed until frothy. Add 1/2 cup of the sugar, 1 Tablespoon at a time, beating until the meringue forms stiff, glossy peaks. Beat the egg yolks in a small bowl with the electric mixer and the same beaters, without washing, until light. Add the remaining sugar 1 tablespoon at a time, beating until mixture is thick and creamy. Add lemon juice and rind. By hand, add the flour mixture gradually, beating until smooth. Fold egg mixture into meringue until no streaks of white remain. Spread batter evenly in prepared pan. Bake in a moderate oven 350~, for 15 minutes or until cake springs back when lightly touched with fingertips. Cool in pan on wire rack 5 minutes. Invert pan on a clean cloth that has been generously sprinkled with confectioners sugar. Carefully peel off paper. Trim off any crispy edges then roll up with towel, starting at one of the short sides. Cool completely on wire rack. Unroll cooled cake; spread with Super Lemon Filling. Re-roll, then wrap firmly in wax paper, refrigerate until firm.

To serve: Remove wax paper, place roll on serving platter and sprinkle with powdered sugar.

For Filling: Combine sugar and cornstarch in a small saucepan. Stir in water. Cook, stirring constantly until mixture thickens and bubbles, 1 minute. Remove from heat. Beat half the hot cornstarch mixture into beaten egg yolks, then stir back into saucepan. Cook one minute longer. Stir in butter, lemon rind and juice. Place piece of plastic wrap directly on filling to prevent skin forming. Refrigerate until ready to use.